Conventionally, a battery assembly (battery module) formed by coupling in series plural unit cells each formed by a secondary battery is divided into plural blocks each including a plurality of the cells, and a voltage detection apparatus includes a plurality of voltage detection units each detecting the cell voltage at each block (see FIG. 1).
FIG. 8 is a diagram showing the configuration of a voltage detection unit of a related art. The voltage detection unit 100 is configured by a high-voltage side circuit 110 and a low-voltage side circuit 120. The high-voltage side circuit is connected to a block 150 formed by secondary batteries and is supplied with power from the block 150 via a power supply line 155. The low-voltage side circuit is connected to an ignition switch 141 and is supplied with power via the ignition switch 141.
The high-voltage side circuit 110 is provided with a voltage detection circuit 111, a 5 volt power supply circuit 112, a logic circuit 113 and an insulation communication IC 114. The low-voltage side circuit 120 is provided with a 5 volt power supply circuit 121, a CPU 122 and an interface (I/F) 123.
In a turned-on state of the ignition switch 141, in the low-voltage side circuit 120, the CPU 122 driven by the 5 volt power supply circuit 121 instructs the detection of the voltage of each of the cells within the block 150 via the insulation communication IC 114. In the high-voltage side circuit 110, the voltage detection circuit 111 detects the voltage of each of the cells within the block 150 in accordance with the instruction.
When the ignition switch 141 is turned off and the power supply is interrupted, in the low-voltage side circuit 120, a value of a current (dark current) flowing through the ignition switch 141 becomes 0. Simultaneously, the high-voltage side circuit 110 also shifts to a sleep state.
As the related art of this kind, a PTL (patent literature) 1 discloses that a secondary battery having a large voltage reduction ratio is connected to a cell control circuit having a small dark current, whilst a secondary battery having a small voltage reduction ratio is connected to a cell control circuit having a large dark current, whereby the voltage reduction ratio of each of the secondary batteries is absorbed by the voltage reduction ratios of the dark currents of the cell control circuits to thereby reduce the degree of the dispersion.
A PTL 2 discloses that control power supplies are respectively connected between power supply input terminals and ground terminals in a state that differential amplifiers are divided into groups and the groups are insulated from each other, to thereby reduce the degree of the dispersion of dark currents.
A PTL 3 discloses that battery cells as one unit are controlled by a cell monitoring IC chip and a control IC chip as a pair.